In connection with roads and particularly large ones for traffic at high speeds, such as motorways and expressways, it is frequently desirable to separate the carriageways by some sort of collision-preventing shielding or crash barrier. This applies specifically between carriageways with traffic in opposite directions, for instance in the middle of the road, to prevent vehicles from coming over, by mistake or in accidents, to the carriageway where vehicles come from the other direction at the risk of the vehicles crashing head-on.
Moreover, it has recently become more and more common to build alternative motorways at a lower cost where carriageways with traffic in opposite directions are not separated by a broad central reserve in the form of e.g. a bank or a ditch, such as on conventional motorways, but such opposite carriageways adjoin each other. Since on such motorways the vehicles frequently travel at high speed and, consequently, a head-on collision becomes devastating, it is usually a requirement that some sort of crash barrier be arranged between carriageways with vehicles coming from opposite directions.
Different types of crash barrier to be used as a shielding separating the carriageways are already known. The most common type is a barrier in the form of elongate, horizontal beams or sections which are mounted on posts buried in the roadway. Such barriers are disadvantageous since they are expansive and time-consuming both to mount and to repair after being damaged, and they have poor collision properties since vehicles striking against them usually bounce back into their own carriageway at the risk of colliding with vehicles travelling in the same direction. Furthermore, the posts themselves-constitute a security risk since they are basically stationary obstacles having a small capability, or none at all, of deformation and gentle absorption of collision forces.
A different type of crash barrier, which recently has become more and more frequent, is wires stretched between posts buried in the roadway. This type of crash barrier suffers from essentially the same drawbacks as the above-mentioned ones. Besides, wires are highly elastic and can, to a still greater degree than crash barriers, cause a vehicle to be thrown back on the carriageway from where it is coming. At high speeds, narrow wires moreover obtain cutting properties which may cause severe damage both to materials and to people.
It is also known to assemble a crash barrier of homogeneous and heavy concrete wall elements. The concrete elements comprise an upwardly extending wall portion and a lower base portion. The crash barrier is composed of a plurality of such barrier elements successively arranged in a row, the base portions being arranged directly on the roadway. The short sides of the barrier elements are connected with cooperating grooves and flanges. Such crash barriers are based on the principle that their mass is to be so great that in a collision they are not dislodged at all or at least but to a very small extent. In a possible collision, they will therefore act as a solid wall with no possibility of soft absorption of the collision forces. If an individual barrier element is dislodged to a very small extent, its short sides, however, will be uncovered, which, besides being sharp, act most unresiliently when being struck since they are supported by a plurality of barrier elements arranged in a row behind the first one. Such barrier elements are, owing to their great mass per unit of length, expensive to buy and time-consuming to mount. However, they are also costly and time-consuming to repair after a collision since individual barrier elements cannot be easily exchanged because of the grooves and flanges which engage each other.
U.S. Pat. No. 4,828,427 discloses a crash barrier according to the preamble to claim 1. In this crash barrier, the barrier elements are made of concrete and interconnected by an articulated connection which consists of two connecting elements projecting from the short sides of each barrier element in the form of a bracket. Through holes are formed in the brackets so that two neighbouring barrier elements can be connected to each other by means of a rod extending through the holes in the brackets. As a result, the barrier elements are articulated to each other, and if a vehicle strikes against the crash barrier, it can be deformed without the barrier elements being separated from each other. One of the brackets connected in pairs has an elongate hole, which means that there is a clearance between the hole in the connecting element and the rod extending through the holes. This clearance makes it possible for the barrier elements to be displaced a limited distance in the longitudinal direction relative to each other. The articulated connection further comprises a spring element which puts two neighbouring barrier elements in an intermediate starting position from which the barrier elements are movable both towards and away from each other. The brackets are connected with the barrier elements by means of a nut which is screwed onto threaded pin ends projecting from each barrier element. In case of a collision, the articulated connections will be exposed to extreme forces, and in the articulated connection construction disclosed in the above-mentioned US patent specification there is a great risk that the brackets and the rods will be deformed if a vehicle strikes against the crash barrier. When restoring the barrier after a collision, it may therefore be necessary to repair the barrier-elements and exchange damaged parts, in certain cases even entire barrier elements. Among other things, the clearance between the throughgoing rod and the holes in the brackets will expose the articulated connections to great impact forces. There is also a great risk that the posts to which the brackets are attached will be pulled out of the concrete. In serious cases, there is also a risk that the articulated connections will break in case of a collision, which causes the barrier elements to be completely separated from each other and the collision-protecting properties of the barrier thus deteriorating to a considerable extent. By the articulated connection having a spring element which puts two neighbouring barrier elements in an intermediate starting position, two neighbouring barrier elements will in the starting position be spaced apart to a certain degree. Apart from this, it would besides not be possible to put the barrier elements closely together since in that case the rod could not be contained between them. This is disadvantageous on the one hand from the aesthetic point of view and, on the other hand, owing to the fact that a colliding vehicle runs the risk of getting stuck in the relatively wide joints.